Typical gas turbine engine fuel supply systems include a fuel source, such as a fuel tank, and one or more pumps that draw fuel from the fuel tank and deliver pressurized fuel to the fuel manifolds and fuel nozzles in the engine combustor via a main supply line. These pumps may include an aircraft or tank level pump, a boost pump, and a high pressure pump. The boost pump is typically a centrifugal pump and the high pressure pump is typically a gear pump, though in some applications the high pressure pump may also be a centrifugal pump. In aircraft fuel systems, the pressurized fuel is provided from the boost pump to the high pressure pump.
Gear pumps generally include a pump housing, with a first gear and a second gear disposed in the pump housing. The first gear and the second gear have gear teeth that are meshed in a mesh region, with rotation of the first gear and the second gear pressurizing liquid feed, such as fuel in the fuel supply systems. In this regard, the pump housing generally defines an inlet cavity adjacent to the first gear and the second gear on one side of the mesh region, and a pump outlet adjacent to the first gear and the second gear on an opposite side of the mesh region from the inlet cavity. The pump outlet includes high pressure liquid feed due to pressurization of the liquid feed by rotation of the first gear and the second gear, whereas the inlet cavity includes liquid feed at lower pressures than at the pump outlet.
The first gear and the second gear each generally include trunnions on opposite sides of the first gear and the second gear for supporting the first gear and the second gear during rotation. Due to rotation of the first gear and the second gear, the trunnions generally generate high temperatures attributable to friction, and a cooling flow of liquid feed is generally employed to cool the trunnions. The trunnions are generally cooled by returning a portion of the high pressure liquid feed from the pump outlet, along a surface of the trunnions, and out to the inlet cavity, thereby exploiting a pressure differential between the pump outlet and the inlet cavity to drive flow of the liquid feed along the surface of the trunnions. However, cooling the trunnions with high pressure liquid feed from the pump outlet negatively impacts pump efficiency.
Other techniques for cooling trunnions in gear pumps have been proposed that employ liquid feed from the inlet cavity. One such technique relies upon low pressure zones created in the mesh region as the gear teeth separate to draw liquid feed into channels disposed in the mesh region and that urge the liquid feed from the inlet cavity to the surface of the trunnions. Another such technique relies upon location of channels that provide liquid feed to the surface of the trunnions in an inertial flow path of liquid feed into the inlet cavity, with suction from rotation of the first gear and second gear drawing the liquid feed into the inlet cavity and with inertia of the liquid feed causing the liquid feed to flow into the channels instead of to the first gear and the second gear. However, such techniques often provide inconsistent cooling of the trunnions because the rate of fluid flow to the trunnions is dependent upon multiple factors, including the rotational speed of the gears and dynamic fluid flow profiles within the gear pumps.
Accordingly, it is desirable to provide a gear pump that promotes efficiency in pressurizing liquid feed, such as fuel, by cooling the trunnions with liquid feed from a low-pressure inlet cavity of the gear pump, while avoiding inconsistent cooling associated with existing gear pumps that cool trunnions with liquid feed from the low-pressure inlet cavity. It is also desirable to provide a pumping apparatus and an aircraft fuel system including the gear pump. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.